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<HTML
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><TITLE
>linux/init/main.c</TITLE
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>Linux i386 Boot Code HOWTO</TH
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><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="init_main"
></A
>7. linux/init/main.c</H1
><P
>&#13; I felt guilty writing this chapter as there are too many documents
about it, if not more than enough.
<EM
>start_kernel()</EM
> supporting functions
are changed from version to version, as they depend on
OS component internals, which are being improved all the time.
I may not have the time for frequent document updates,
so I decided to keep this chapter as simple as possible.
</P
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="start_kernel"
></A
>7.1. start_kernel()</H2
><P
>&#13;<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="programlisting"
>///////////////////////////////////////////////////////////////////////////////
<A
HREF="http://kernelnewbies.org/faq/index.php3#asmlinkage"
TARGET="_top"
>asmlinkage</A
> void <A
HREF="http://www.tldp.org/LDP/lki/lki-1.html#ss1.8"
TARGET="_top"
>__init</A
> start_kernel(void)
{
char * command_line;
extern char saved_command_line[];
/*
* Interrupts are still disabled. Do necessary setups, then enable them
*/
lock_kernel();
printk(linux_banner);
/* <A
HREF="http://www.symonds.net/~abhi/files/mm/mm.html"
TARGET="_top"
>Memory Management in Linux</A
>, esp. for setup_arch()
* <A
HREF="http://linux-mm.org/docs/initialization.html"
TARGET="_top"
>Linux-2.4.4 MM Initialization</A
> */
setup_arch(&#38;command_line);
printk("Kernel command line: %s\n", saved_command_line);
/* <TT
CLASS="filename"
>linux/Documentation/kernel-parameters.txt</TT
>
* <A
HREF="http://www.tldp.org/HOWTO/BootPrompt-HOWTO.html"
TARGET="_top"
>The Linux BootPrompt-HowTo</A
> */
parse_options(command_line);
trap_init() {
#ifdef CONFIG_EISA
if (isa_readl(0x0FFFD9) == 'E'+('I'&#60;&#60;8)+('S'&#60;&#60;16)+('A'&#60;&#60;24))
EISA_bus = 1;
#endif
#ifdef CONFIG_X86_LOCAL_APIC
init_apic_mappings();
#endif
set_xxxx_gate(x, &#38;func); // setup gates
cpu_init();
}
init_IRQ();
sched_init();
softirq_init() {
for (int i=0; i&#60;32: i++)
tasklet_init(bh_task_vec+i, bh_action, i);
open_softirq(TASKLET_SOFTIRQ, tasklet_action, NULL);
open_softirq(HI_SOFTIRQ, tasklet_hi_action, NULL);
}
time_init();
/*
* HACK ALERT! This is early. We're enabling the console before
* we've done PCI setups etc, and console_init() must be aware of
* this. But we do want output early, in case something goes wrong.
*/
console_init();
#ifdef CONFIG_MODULES
init_modules();
#endif
if (prof_shift) {
unsigned int size;
/* only text is profiled */
prof_len = (unsigned long) &#38;_etext - (unsigned long) &#38;_stext;
prof_len &#62;&#62;= prof_shift;
size = prof_len * sizeof(unsigned int) + PAGE_SIZE-1;
prof_buffer = (unsigned int *) alloc_bootmem(size);
}
kmem_cache_init();
sti();
// <A
HREF="http://www.tldp.org/HOWTO/BogoMips.html"
TARGET="_top"
>BogoMips mini-Howto</A
>
calibrate_delay();
// <TT
CLASS="filename"
>linux/Documentation/initrd.txt</TT
>
#ifdef CONFIG_BLK_DEV_INITRD
if (initrd_start &#38;&#38; !initrd_below_start_ok &#38;&#38;
initrd_start &#60; min_low_pfn &#60;&#60; PAGE_SHIFT) {
printk(KERN_CRIT "initrd overwritten (0x%08lx &#60; 0x%08lx) - "
"disabling it.\n",initrd_start,min_low_pfn &#60;&#60; PAGE_SHIFT);
initrd_start = 0;
}
#endif
mem_init();
kmem_cache_sizes_init();
pgtable_cache_init();
/*
* For architectures that have highmem, num_mappedpages represents
* the amount of memory the kernel can use. For other architectures
* it's the same as the total pages. We need both numbers because
* some subsystems need to initialize based on how much memory the
* kernel can use.
*/
if (num_mappedpages == 0)
num_mappedpages = num_physpages;
fork_init(num_mempages);
proc_caches_init();
vfs_caches_init(num_physpages);
buffer_init(num_physpages);
page_cache_init(num_physpages);
#if defined(CONFIG_ARCH_S390)
ccwcache_init();
#endif
signals_init();
#ifdef CONFIG_PROC_FS
proc_root_init();
#endif
#if defined(CONFIG_SYSVIPC)
ipc_init();
#endif
check_bugs();
printk("POSIX conformance testing by UNIFIX\n");
/*
* We count on the initial thread going ok
* Like idlers init is an unlocked kernel thread, which will
* make syscalls (and thus be locked).
*/
smp_init() {
#ifndef CONFIG_SMP
# ifdef CONFIG_X86_LOCAL_APIC
APIC_init_uniprocessor();
# else
do { } while (0);
# endif
#else
/* Check <A
HREF="smpboot.html#smp_init"
>Section 8.2</A
>. */
#endif
}
rest_init() {
// init process, pid = 1
kernel_thread(init, NULL, CLONE_FS | CLONE_FILES | CLONE_SIGNAL);
unlock_kernel();
current-&#62;need_resched = 1;
// idle process, pid = 0
cpu_idle(); // never return
}
}</PRE
></FONT
></TD
></TR
></TABLE
>
<EM
>start_kernel()</EM
> calls <EM
>rest_init()</EM
>
to spawn an "init" process and become "idle" process itself.
</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="init_proc"
></A
>7.2. init()</H2
><P
>&#13; "Init" process:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="programlisting"
>///////////////////////////////////////////////////////////////////////////////
static int init(void * unused)
{
lock_kernel();
do_basic_setup();
prepare_namespace();
/*
* Ok, we have completed the initial bootup, and
* we're essentially up and running. Get rid of the
* initmem segments and start the user-mode stuff..
*/
free_initmem();
unlock_kernel();
if (open("/dev/console", O_RDWR, 0) &#60; 0) // stdin
printk("Warning: unable to open an initial console.\n");
(void) dup(0); // stdout
(void) dup(0); // stderr
/*
* We try each of these until one succeeds.
*
* The Bourne shell can be used instead of init if we are
* trying to recover a really broken machine.
*/
if (execute_command)
execve(execute_command,argv_init,envp_init);
execve("/sbin/init",argv_init,envp_init);
execve("/etc/init",argv_init,envp_init);
execve("/bin/init",argv_init,envp_init);
execve("/bin/sh",argv_init,envp_init);
panic("No init found. Try passing init= option to kernel.");
}</PRE
></FONT
></TD
></TR
></TABLE
>
Refer to "<B
CLASS="command"
>man init</B
>" or
<A
HREF="http://freshmeat.net/projects/sysvinit"
TARGET="_top"
>SysVinit</A
>
for further information on user-mode "init" process.
</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="idle_proc"
></A
>7.3. cpu_idle()</H2
><P
>&#13; "Idle" process:
<TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
WIDTH="100%"
><TR
><TD
><FONT
COLOR="#000000"
><PRE
CLASS="programlisting"
>/*
* The idle thread. There's no useful work to be
* done, so just try to conserve power and have a
* low exit latency (ie sit in a loop waiting for
* somebody to say that they'd like to reschedule)
*/
void cpu_idle (void)
{
/* endless idle loop with no priority at all */
init_idle();
current-&#62;nice = 20;
current-&#62;counter = -100;
while (1) {
void (*idle)(void) = pm_idle;
if (!idle)
idle = default_idle;
while (!current-&#62;need_resched)
idle();
schedule();
check_pgt_cache();
}
}
///////////////////////////////////////////////////////////////////////////////
void __init init_idle(void)
{
struct schedule_data * sched_data;
sched_data = &#38;aligned_data[smp_processor_id()].schedule_data;
if (current != &#38;init_task &#38;&#38; task_on_runqueue(current)) {
printk("UGH! (%d:%d) was on the runqueue, removing.\n",
smp_processor_id(), current-&#62;pid);
del_from_runqueue(current);
}
sched_data-&#62;curr = current;
sched_data-&#62;last_schedule = get_cycles();
clear_bit(current-&#62;processor, &#38;wait_init_idle);
}
///////////////////////////////////////////////////////////////////////////////
void default_idle(void)
{
if (current_cpu_data.hlt_works_ok &#38;&#38; !hlt_counter) {
__cli();
if (!current-&#62;need_resched)
safe_halt();
else
__sti();
}
}
/* defined in linux/include/asm-i386/system.h */
#define __cli() __asm__ __volatile__("cli": : :"memory")
#define __sti() __asm__ __volatile__("sti": : :"memory")
/* used in the idle loop; sti takes one instruction cycle to complete */
#define safe_halt() __asm__ __volatile__("sti; hlt": : :"memory")</PRE
></FONT
></TD
></TR
></TABLE
>
CPU will resume code execution with the instruction following "hlt"
on the return from an interrupt handler.
</P
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="main_ref"
></A
>7.4. Reference</H2
><P
>&#13; <P
></P
><UL
><LI
><P
><A
HREF="http://www.tldp.org/LDP/lki/index.html"
TARGET="_top"
>&#13; Linux Kernel 2.4 Internals</A
></P
></LI
><LI
><P
><A
HREF="http://kernelnewbies.org/documents/"
TARGET="_top"
>&#13; Kerneldoc</A
></P
></LI
><LI
><P
><A
HREF="http://www.tldp.org/HOWTO/HOWTO-INDEX/index.html"
TARGET="_top"
>&#13; LDP HOWTO-INDEX</A
></P
></LI
><LI
><P
><A
HREF="http://www.xml.com/ldd/chapter/book"
TARGET="_top"
>&#13; Linux Device Drivers, 2nd Edition</A
></P
></LI
></UL
>
</P
></DIV
></DIV
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>
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